1. Field of the Invention
This invention relates to a washing machine or a combination wash dryer with an automatic detergent dispensing apparatus and a washwater pump which evacuates the washwater via a drain hose, and with equipment to prevent detergent losses. An advantageous method to control this washing machine is also described.
2. Description of the Prior Art
A longstanding goal of the washing machine industry has been to keep the amount of detergent not used in the washing process as low as possible. A number of different proposals have been made to solve this probem. DE-OS No. 31 06 604 and DE-GM No. 78 13 695 describe arrangements in which there is a so-called float in the washtub drain, which floats upward as a result of the backpressure of the remaining water in the drain hose, and is thereby intended to close the drain opening.
Such closing devices have not been realized in practice, however, since it has proven to be very difficult to achieve a really tight seal at the drain opening. Even a small leak sooner or later leads to an equalization of the remaining water column in the drain hose, i.e. the water gets into the tub and the bouyancy of the hollow body is no longer sufficient to achieve a secure closing of the drain opening. In the subsequent wash cycle, nevertheless, detergent can still get through the drain opening into the sump of the machine, and therefore becomes useless for the washing process.
Another valve configuration for the same purpose is described in DE-PS No. 27 12 093. The flap valve described therein is expensive, and is complicated to install in the washtub drain. Furthermore, lint or similar substances can easily prevent a complete closing.
The prior art also includes an additional reservoir in the drain system of a washing machine, so that there will always be enough water remaining in the drain system to prevent the dispensed detergent from sinking down into the drain.
But even this measure has proven ineffective. The detergent, generally in granular form, still gets into the area of the drain before it is dissolved, and is removed unused during drainage.
Thus all previous efforts to prevent detergent losses in the manner described above have been unsuccessful.